Internal combustion engines of the type cited in the introduction are used in particular as vehicle drives. In addition they are also suited to use in light aircraft and boats.
It is known from DE 10 2004 038 338 B3 to determine the air mass supplied to the engine by means of a mass air flow meter, for example a hot-wire anemometer. The air mass supplied to the engine can then be regulated by means of a throttle valve and/or through adjustment of the valve opening times and/or the valve lift. In a spark-ignited internal combustion engine having exhaust gas aftertreatment it is usually desired to set the fuel/air ratio λ to the stoichiometric ratio (λ=1). Thus, the amount of fuel that is to be injected, and hence the energy conversion per power stroke, is also defined, based on a predetermined air mass. The setpoint value for the air mass can therefore be determined directly by an engine control unit from the torque setpoint value.
It is also known from Beer, M. et al, MTZ Motortechnische Zeitschrift, 61 (2000) 11, p. 730, to adapt an internal combustion engine to different operating states through provision of a two-stage or multistage valve lift switchover means. For example, an electrohydraulic valve lift switchover can be implemented in that a locking element in a control bucket tappet or a rocker arm is actuated by means of oil pressure against a spring and thus, according to the activation or deactivation status, switches between two different valve lift curves. To effect the switchover, an electric current is applied to an electromagnetic valve (3/2-way valve) located in the oil circuit, the valve thereupon opening. The oil pressure builds up and the locking element moves against the spring until the locking operation is completed. When the electromagnetic valve is closed again, the oil pressure dissipates via a leakage line and the locking element, activated by the spring force, slides back into its starting position.
This enables a large volume of air to be supplied in the full load (wide-open throttle) operating range, said volume of air being required in order to deliver a high torque. During partial load operation the valve lift can be reduced in order to supply a smaller air mass to the cylinder. By reducing the opening stroke of the intake valves it is possible, while maintaining the same torque delivery, to open the throttle valve disposed in the intake manifold wider in order to reduce throttle losses thereby.
During the switchover from one valve lift to another valve lift measures must be taken in order to keep the torque delivered before and after the switching operation constant. Otherwise the switching operation would be experienced as unpleasant by the user. Toward that end an intervention to alter the ignition angle is used in order to reduce the engine torque that is output. The aspirated air mass can subsequently be adjusted by way of the throttle valve. A disadvantage with this approach, however, is that during the switchover the engine will not be operated in the consumption-optimized operating state for several power cycles.
It is known from DE 10 2004 061 143 A1 to minimize the torque jump occurring during the valve lift switchover before and after the switching operation by initially outputting a control signal to the throttle valve and triggering the valve lift switchover at a later time which is determined from the dead time and the run time of the filling intervention as well as the switchover duration of the final control elements for the valve lift switchover.
It is known from 10 2004 061 142 A1 to adjust the throttle valve position in accordance with a decreasing ramp function already before the switchover of the valve lift takes place. The torque, increasing or decreasing due to the changed throttle valve position, is compensated by adjusting the injected fuel quantity. The valve lift switchover is performed at an operating point at which a compensation of the torque curve through variation of the supplied fuel quantity is no longer possible. Torque differences remaining after the valve lift switchover are corrected by means of an ignition angle intervention.